Getting this question right is the essence of salvation and is also the starting point for a lifelong journey. You are saved when you come to know and believe in Jesus as your Lord and Savior ( Romans 10:9-10) but that is only the beginning of your relationship with Him.
As Peter correctly identified and recognized who Jesus was, Jesus in turn praises and identifies who Peter is when He says in verse 17-18, "Blessed art thou, Simon Bar–jona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven. And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.”
He is basically saying to Peter, "You are favored Simon, because man did not tell you that but God revealed and communicated that to you!" He then changes his name and identity to his new name and nature; just as he did with so many in the Bible like: Abram to Abraham, Sarai to Sarah, Jacob to Israel, and Saul to Paul to name a few. Now Jesus isn't saying Peter is the rock, but Peter's answer of who Jesus is, is the foundation or rock that the church would be built on. He wanted Peter to remember that his new identity, like ours as Christians, is in Jesus!
So today, who do you say Jesus is? Who is He to you? Is He your savior today? Do you know Him personally and have a relationship with Him? If not He longs to have a relationship with you because He loves you. And I would be honored to talk more with you about it!